In recent years, with the advancement of personal computers and wide-screen liquid crystal televisions, the demand for liquid crystal displays (LCDs), in particular for liquid crystal color displays has tended to increase. Further, due to the demand for much higher image quality, the popularization of organic EL displays has been eagerly awaited.
Meanwhile, the demand for solid-state image sensors such as CCD image sensors has been significantly growing in accordance with the popularization of digital cameras, camera-equipped mobile phones and the like. Color filters have been used as a key device of such displays or optical devices, and the demand for cost reduction of color filters has been increasing in conjunction with the demand for higher image quality.
A color filter used for an mage display device or a solid-state image sensor generally has a color pattern of three primary colors, red (R), green (G), and blue (B), and serves to color the transmitting light or separate it into the three primary colors.
Coloring agents used in the color filter are commonly required to have the following characteristics. That is, they are required to have preferable light absorption characteristics in view of color reproducibility, to exhibit no occurrence of optical disturbance such as light scattering responsible for lowering of contrast in liquid crystal displays or non-uniformity of an optical density responsible for color unevenness or rough feeling in solid-state image sensors, to have favorable resistance for the environmental conditions under which they are used, such as, for example, heat resistance, light fastness and resistance to moist heat, and to provide a large molar absorption coefficient and the possibility of thickness reduction.
Examples of the methods of manufacturing the color filter used for liquid crystal displays, solid-state image sensors, or the like include a pigment dispersing method. Specific examples of the pigment dispersing method include a method of manufacturing a color filter by the use of a photolithographic method using a colored radiation-sensitive composition, in which a pigment is dispersed in various photosensitive compositions. More specifically, a radiation-sensitive composition is coated on a substrate using a spin coater, a roll coater or the like, and is dried, thereby forming a coated film. The coated film is exposed in a pattern-wise manner and developed, thereby obtaining colored pixels. The operation is repeated in desired numbers of color hues, thereby manufacturing a color filter.
The above method has been widely used as a method of manufacturing a color filter for color displays or the like, because, in the method, the color filter, which is formed using a pigment, is stable against heat or light, and patterning is performed by a photolithographic method, so that positioning accuracy can sufficiently be secured.
Liquid crystal displays have been widely used as television screens, computer screens or other display devices, since liquid crystal displays are compact and achieve power-saving as display devices and have equivalent or better function compared with conventional display devices
In recent years, the development of liquid crystal displays has expanded from application for computer screens or monitors, which have relatively small surface areas, to application for TV screens, which have large surface areas and require high image quality.
In the application for TV screens, higher image quality compared with conventional monitors, that is, improved contrast and color purity, has been demanded. In order to improve the contrast, photosensitive resin compositions for forming color filters are required to contain colorants (organic pigments or the like) having a smaller particle size. Furthermore, in order to improve color purity, it is important to increase the content of the colorants (organic pigments or the like) with respect to the solid content of the photosensitive resin compositions. However, conventional pigment dispersing methods are not sufficient for these requirements.
Furthermore, in recent years, higher definition in color filters for solid-state image sensors such as a CCD or the like has been demanded. Accordingly, micronization of pigments has been desired in order to suppress the color unevenness caused by coarse particles of pigments. Further, in a liquid crystal display, an organic EL display and the like, a color filter manufactured by the photolithographic method using a pigment dispersing method has the advantages that light fastness and heat resistance are excellent, but has the problems that a decrease in contrast or an increase in haze resulting from light scattering due to coarse particles of pigment arise. Therefore, in a color filter for a liquid crystal display, an organic EL display or the like, micronization of pigment particles has been desired.
However, since fine particles of a pigment are apt to aggregate, it is necessary to impart dispersibility to pigment. With an increase in definition, the size of a pattern tends to be micronized, but it is thought that it will be difficult to further micronize the pattern size, and to further enhance the resolution, by using the widely used pigment dispersing methods. One of the reasons for this is that, in a minute pattern, color unevenness is caused by coarse particles formed by aggregation of pigment particles. Accordingly, in recent years, a situation has been reached where the pigment dispersing methods, which have been widely used, are not necessarily suitable for use in, for example, solid-state image sensors requiring a minute pattern.
Under such circumstances, a technique using a dye in place of a pigment has been suggested (for example, see Japanese Patent Application Laid-Open (JP-A) No. 6-75375). When a dye is used in place of the pigment, color filters for solid-state image sensors are expected to achieve high resolution by solving the problems of color unevenness and rough feeling, whereas liquid crystal displays or organic EL displays are expected to achieve improvements in optical properties such as contrast or haze. In addition, the inkjet method using a dye generally has high jetting stability and is expected to achieve easy recovery of an ink jetting state by wiping or purging even when there is nozzle clogging associated with an increased ink viscosity or the like.
However, a dye-containing colored curable composition has other problems as follows.
(1) Dyes in a molecular dispersed state are generally poor in light fastness and heat resistance as compared to pigments forming molecular aggregates. In particular, there is a problem in that optical properties are changed due to a high-temperature process when forming a film of indium tin oxide (ITO) widely used as an electrode for liquid crystal displays or the like.
(2) Dyes in a molecular dispersed state are generally poor in solvent resistance as compared to pigments forming molecular aggregates.
(3) Dyes tend to inhibit a radical polymerization reaction, so there is difficulty in designing of a colored curable composition, for a system where radical polymerization is used as a curing means.
(4) Conventional dyes exhibit low solubility in an alkaline aqueous solution or organic solvent (hereinbelow, also referred to simply as “solvent”), and thus, it is difficult to obtain a colored curable composition with a desired spectrum.
(5) Dyes often exhibit interaction with other components in the colored curable composition, so it is difficult to control the solubility (developability) of the exposed parts and the non-exposed parts.
(6) When a molar absorption coefficient (∈) of the dye is low, a large amount of the dye needs to be added. Therefore, the amount of other components such as a polymerizable compound (monomer), a binder or photopolymerization initiator in the colored curable composition has to be relatively decreased, thereby reducing the curability, post-curing heat resistance, and developability of the composition.
Among these problems related to dyes, dipyrromethene metal complexes have been studied as dyes that solve the problems in item (1) above related to light fastness and heat resistance of dyes, and in item (6) above related to the molar absorption coefficient (∈) of dyes (for example, see U.S. Patent Publication No. 2008/0076044).
In a polymerizable composition that polymerizes with visible light, dipyrromethene metal complexes are used as a functional compound in addition to a sensitizer for a radical polymerization initiator (for example, see Japanese Patent Nos. 3279035, and 3324279, and JP-A Nos. 11-352685, 11-352686, 2000-19729, 2000-19738, and 2002-236360). It is reported that the dipyrromethene metal complexes have excellent light fastness and heat resistance, a high molar absorption coefficient (∈), and preferable light absorption characteristics in view of color reproducibility (for example, see U.S. Patent Application Publication No. 2008/0076044).
Because of these problems, it ha s been difficult hitherto to form a color pattern for high-definition color filters, which is composed of a fine thin film and has excellent resistance, using a dye. In addition, with regard to color filters for solid-state image sensors, a colored layer is required to be formed of a thin film having a thickness of 1 μm or less. Therefore, in order to achieve desired absorption, a large amount of the colorant needs to be added to the curable composition, consequently resulting in the aforementioned problems.
Further, with regard to a colored curable composition containing a dye, it has been pointed out that, when a heating treatment is applied after the formation of a film, color transfer readily occurs between adjacent differently color patterns or between stacked and overlapped layers. In addition to color transfer, pattern peeling readily takes place in a low-exposure dose region due to the decreased sensitivity, and a desired shape or color density cannot be obtained due to thermal sagging, elution upon development, or the like which is caused by the decrease in the relative amount of photosensitive components contributing to photolithographic properties.
As approaches to solve these problems, there have been conventionally proposed a variety of methods involving selecting the kind of initiators, increasing an addition amount of initiators, or the like (for example, see JP-A No. 2005-316012). Further, there has been disclosed a method of producing a color filter wherein a color pattern is formed, and then polymerization is carried out in an elevated exposure temperature state by irradiating light to the color pattern while heating a substrate, thus increasing a polymerization rate of the system (for example, see Japanese Patent No. 3309514). In addition, there has been disclosed a method of producing a color filter wherein light irradiation is carried out between a development treatment and a heating treatment, thereby preventing shape deformation of the color filter (for example, see JP-A No. 2006-258916).
Furthermore, the conventional dyes are problematic in that the dyes exhibit low developability in an alkaline solution, and thus a colored curable composition including such a dye exhibits low solubility (developability) in the non-exposed parts, which impairs pattern formation. As approaches to solve this problem, a method of polymerizing dyes by copolymerizing a monomer having a colorant group and a monomer having an alkali-soluble group in order to impart developability to a dye has been disclosed (for example, see JP-A Nos. 2007-139906 and 2007-138051, and Japanese Patent No 3736221).